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5 Types of Extraneous Variables

Extraneous variables are any factors that can influence an experiment that aren't the independent variables that you are testing. Ideally, all extraneous variables are controlled using techniques such as controlled variables, negative control groups and positive control groups. The following are common types of extraneous variable.


Variables related to the situation such as the amount of light, wind, water and soil composition in an experiment on plants.


Variables related to participants such as the age and gender of people in a medical study.

Demand Characteristics

What participants know about the research. For example, in a psychology study participants may change responses to fit what they think is expected.


Variables related to the people conducting the experiment. For example, an experiment where seven researchers take proper measurements and an eight researcher takes incorrect measurements because they have a fundamental misunderstanding about the equipment or process used in the measurement.

Confounding Variable

A confounding variable is a variable that influences both the independent and dependent variables in an experiment. This is often a flaw in experimental procedures or equipment. For example, an experiment on a plant fertilizer where too much water is applied to the plants causing the fertilizer to run off and the plants to die.
Overview: Extraneous Variables
Variables that can influence an experiment that aren't the independent variables that you are testing.
Related Concepts


This is the complete list of articles we have written about experiments.
Alternative Hypothesis
Control Group
Dependent Variable
Empirical Evidence
Experiment Design
Experimental Error
Explanatory Power
Natural Experiment
Negative Control
Negative Correlation
Null Hypothesis
Original Research
Positive Control
Positive Correlation
Primary Research
Qualitative Info
Random Assignment
Random Error
Scientific Control
Scientific Fact
Soft Science
Systematic Error
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